Equipment of all types is often formed of a combination of diverse materials, such as metals, plastics, and ceramics. Examples include lighting devices; power equipment, e.g., gas turbine engines for land and flight applications; pumps used in oil and gas exploration; spectroscopic devices; and medical equipment, such as X-ray devices. Another example involves electrochemical devices such as batteries and fuel cells. Structures within these devices need to be joined to each other in a way that provides a seal on or within the particular device. Brazing is a widely-used joining method suitable for many of these applications.
The gas turbine engines mentioned above are used in a variety of advanced military and commercial aircraft, as well as power generation plants. The engines often include components that need to be joined together by brazing, e.g., metal-metal joining, metal-ceramic joining, and even ceramic-ceramic-joining. A wide variety of braze compositions have been developed to meet the requirements for many different types of end use applications. As one example, very specialized braze compositions have been developed for joining metal and ceramic components that are used under demanding environmental conditions, including elevated temperatures, e.g., above about 300° C., and sometimes, above about 1,000° C.
Nickel-based braze materials are usually employed for joining nickel-formed components to other components. These materials are often crystalline braze alloys, such as those containing nickel, germanium, and titanium. While such alloys are desirable for many brazing applications, they cannot easily be used and applied in a variety of forms, such as foils, ribbons, and wires. Instead, they often can only be used in the form of powders.
In contrast, braze alloys formed from nickel, boron, and silicon are generally amorphous, and can therefore be used in many forms. These types of alloys are usually characterized as “amorphous glass”. While they are preferred for some applications, there are also some drawbacks associated with the alloy compositions. As an example, the presence of the silicon constituent can lead to the formation of one or more brittle intermetallic phases, which are usually undesirable.
As alluded to previously, metal-ceramic joints are often necessary for a variety of these machines and devices. It has often been difficult to provide braze compositions that can successfully provide such a joint, due in part to CTE differences, as well as the difficulty in wetting the ceramic surface during a brazing operation. One technique for achieving a good ceramic-metal uses an active metal element (e.g., titanium or zirconium) that promotes wetting of a ceramic surface, enhancing the capability of providing a hermetic seal. While this technique is useful for many situations, there are other situations where the use of active brazing may not be desirable or cost-effective.
With these concerns in mind, new braze compositions that are generally free from brittle intermetallic phases would be welcome in the industry. The compositions should be relatively ductile, and capable of being formed into a variety of shapes for brazing. The compositions should also exhibit a high level of strength at elevated temperatures that are prevalent for end uses such as gas turbine engines and thermal batteries.